grpc-golang – Coding skill for AI agents

gRPC Golang (gRPC-Go)

Overview

Comprehensive guide for designing and implementing production-grade gRPC services in Go. Covers contract standardization with Buf, transport layer security via mTLS, and deep observability with OpenTelemetry instrumentation.

Use this skill when

• Designing microservices communication with gRPC in Go.
• Building high-performance internal APIs using Protobuf.
• Implementing streaming workloads (unidirectional or bidirectional).
• Standardizing API contracts using Protobuf and Buf.
• Configuring mTLS for service-to-service authentication.

Do not use this skill when

• Building pure REST/HTTP public APIs without gRPC requirements.
• Modifying legacy .proto files without the ability to introduce a new API version (e.g., api.v2) or ensure backward compatibility.
• Managing service mesh traffic routing (e.g., Istio/Linkerd), which is outside the application code scope.

Step-by-Step Guide

1. Confirm Technical Context: Identify Go version, gRPC-Go version, and whether the project uses Buf or raw protoc.

2. Confirm Requirements: Identify mTLS needs, load patterns (unary/streaming), SLOs, and message size limits.

3. Plan Schema: Define package versioning (e.g., api.v1), resource types, and error mapping.

4. Security Design: Implement mTLS for service-to-service authentication.

5. Observability: Configure interceptors for tracing, metrics, and structured logging.

6. Verification: Always run buf lint and breaking change checks before finalizing code generation.

Refer to resources/implementation-playbook.md for detailed patterns, code examples, and anti-patterns.

Examples

Example 1: Defining a Service & Message (v1 API)

syntax = "proto3";
package api.v1;
option go_package = "github.com/org/repo/gen/api/v1;apiv1";

service UserService {
  rpc GetUser(GetUserRequest) returns (GetUserResponse);
}

message User {
  string id = 1;
  string name = 2;
}

message GetUserRequest {
  string id = 1;
}

message GetUserResponse {
  User user = 1;
}

Best Practices

• ✅ Do: Use Buf to standardize your toolchain and linting with buf.yaml and buf.gen.yaml.
• ✅ Do: Always use semantic versioning in package paths (e.g., package api.v1).
• ✅ Do: Enforce mTLS for all internal service-to-service communication.
• ✅ Do: Handle ctx.Done() in all streaming handlers to prevent resource leaks.
• ✅ Do: Map domain errors to standard gRPC status codes (e.g., codes.NotFound).
• ❌ Don't: Return raw internal error strings or stack traces to gRPC clients.
• ❌ Don't: Create a new grpc.ClientConn per request; always reuse connections.

Troubleshooting

• Error: Inconsistent Gen: If the generated code does not match the schema, run buf generate and verify the go_package option.
• Error: Context Deadline: Check client timeouts and ensure the server is not blocking infinitely in streaming handlers.
• Error: mTLS Handshake: Ensure the CA certificate is correctly added to the x509.CertPool on both client and server sides.

Limitations

• Does not cover service mesh traffic routing (Istio/Linkerd configuration).
• Does not cover gRPC-Web or browser-based gRPC integration.
• Version-specific sketches, not a supported-version matrix; verify current Go/gRPC-Go module requirements and APIs (e.g., grpc.Dial vs grpc.NewClient).
• Does not cover L7 gRPC-aware load balancer configuration (e.g., Envoy, NGINX).
• Does not address Protobuf schema registry or large-scale schema governance beyond Buf lint.

Resources

• resources/implementation-playbook.md for detailed patterns, code examples, and anti-patterns.
• [Google API Design Guide](https://cloud.google.com/apis/design)
• [Buf Docs](https://buf.build/docs)
• [gRPC-Go Docs](https://grpc.io/docs/languages/go/)
• [OpenTelemetry Go Instrumentation](https://opentelemetry.io/docs/instrumentation/go/)

Related Skills

• @golang-pro - General Go patterns and performance optimization outside the gRPC layer.
• @go-concurrency-patterns - Advanced goroutine lifecycle management for streaming handlers.
• @api-design-principles - Resource naming and versioning strategy before writing .proto files.
• @docker-expert - Containerizing gRPC services and configuring TLS cert injection via Docker secrets.